Early on, the Facebook Class became a microcosm of Silicon Valley. Working in teams of three, the 75 students created apps that collectively had 16 million users in just 10 weeks. Many of those apps were sort of silly: Mr. De Lombaert’s, for example, allowed users to send “hotness” points to Facebook friends. Yet during the term, the apps, free for users, generated roughly $1 million in advertising revenue.